Thin film transistor array substrate, organic light-emitting diode display including the same, and manufacturing method thereof

ABSTRACT

A TFT array substrate, OLED display including the same, and a manufacturing method of the OLED display are disclosed. In one aspect, the TFT array substrate includes a substrate and a TFT formed over the substrate. The TFT includes an active layer, a gate electrode, a source electrode, a drain electrode, a first insulating layer interposed between the gate electrode and the source and drain electrodes. Each of the source and drain electrodes is interposed between the active layer and the first insulating layer. The TFT array substrate also includes a capacitor formed over the substrate and having lower and upper electrodes and a pixel electrode electrically connected to the TFT.

RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2014-0154729, filed on Nov. 7, 2014, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND

1. Field

The described technology generally relates to a thin film transistor(TFT) array substrate, an organic light-emitting diode (OLED) displayincluding the TFT array substrate, and a method of manufacturing theOLED display.

2. Description of the Related Technology

OLED displays have drawn attentions for use as next generation displaysfor their wide viewing angles, excellent contrast, and high responserates.

Flat panel display technologies, such as OLED displays and liquidcrystal displays (LCDs), include a matrix of pixels, each having a thinfilm transistor (TFT), a capacitor, and wirings connecting the TFT andthe capacitor. On a substrate on which the FPD is formed, the TFT, thecapacitor, and the wirings are formed in fine patterns, and aphotolithography process, which transfers patterns by using a mask, ismainly used in order to form the fine patterns of the substrate.

In the photolithography process, a photoresist is spread on a substrateon which patterns are to be formed, and the photoresist is exposed tolight by using an exposure device, such as a stepper. Then, adevelopment process is performed on the light-sensitive (positive)photoresist. After the photoresist is developed, patterns on thesubstrate are etched by using the remaining photoresist, and asacrificial photoresist material is removed after the patterns areformed.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

One inventive aspect is a thin film transistor (TFT) array substratewhose manufacturing process is simple and signal transferringcharacteristics are excellent, an OLED display including the TFT arraysubstrate, and a method of manufacturing the OLED display.

Another aspect is a thin film transistor (TFT) array substrate thatincludes a substrate; a TFT formed on the substrate and including anactive layer, a gate electrode, a source electrode, and a drainelectrode, wherein a first insulating layer is interposed between thegate electrode, and the source electrode and the drain electrode, andthe source electrode and the drain electrode are interposed between theactive layer and the first insulating layer; a capacitor formed on thesubstrate and including a lower electrode and an upper electrode; and apixel electrode electrically connected to the TFT.

The lower electrode of the capacitor can include a same material as thatof the source electrode and the drain electrode and can be formed on asame layer as the source electrode and the drain electrode. The upperelectrode of the capacitor can be formed on a same layer as the gateelectrode and can include a same material as the gate electrode.

At least a portion of the active layer can overlap the source electrode,the drain electrode, and the gate electrode. The active layer caninclude a first region which is an area overlapping the source electrodeand the drain electrode, a second region which is an area overlappingthe gate electrode, and a third region which is an area except the firstregion and the second region, wherein only the third region includes animpurity.

The first region can be an area in which the active layer directlycontacts the source electrode and the drain electrode.

The first insulating layer can be formed such that the first insulatinglayer covers the active layer, and the source electrode and the drainelectrode.

The gate electrode can be formed on the first insulating layer, and thefirst insulating layer can be interposed between the gate electrode, andthe source electrode and the drain electrode.

The active layer, the source electrode, and the drain electrode can beintegrally formed.

The TFT array substrate can further include a second insulating layerwhich is formed on the TFT and the capacitor to cover the gate electrodeand the upper electrode.

Another aspect is an OLED display that includes: a substrate; a thinfilm transistor (TFT) formed on the substrate and including an activelayer, a gate electrode, a source electrode, and a drain electrode,wherein a first insulating layer is interposed between the gateelectrode, and the source electrode and the drain electrode, and thesource electrode and the drain electrode are interposed between theactive layer and the first insulating layer; a capacitor formed on thesubstrate and including a lower electrode formed on a same layer as thesource electrode and the drain electrode and an upper electrode formedon a same layer as the gate electrode; a second insulating layer formedon the TFT and the capacitor to cover the gate electrode and the upperelectrode; a pixel electrode electrically connected with the TFT; athird insulating layer exposing a central portion of the pixel electrodeand covering an edge of the pixel electrode; an intermediate layerformed on the pixel electrode and including an emission layer; and anopposite electrode covering the intermediate layer and formed to facethe pixel electrode.

Another aspect is a method of manufacturing an OLED display thatincludes: a first mask process for forming an active layer, a sourceelectrode, and a drain electrode of a thin film transistor (TFT) bysequentially disposing a semiconductor material layer and a first metallayer on a substrate and patterning the semiconductor material layer andthe first metal layer; a second mask process for forming a gateelectrode on a portion of a first insulating layer, which corresponds tothe active layer, after stacking the first insulating layer and a secondmetal layer on the active layer, the source electrode, and the drainelectrode so as to cover the active layer, the source electrode, and thedrain electrode; a third mask process for forming a via-hole exposingany one of the source electrode and the drain electrode of the TFT,after stacking a second insulating layer on the first insulating layerto cover the gate electrode; a fourth mask process for forming a pixelelectrode electrically connected with any one of the source electrodeand the drain electrode of the TFT via the via-hole, by disposing athird metal layer on the second insulating layer; and a fifth maskprocess for forming a third insulating layer on the second insulatinglayer, the third insulating layer exposing a central portion of thepixel electrode by covering an edge of the pixel electrode.

The first mask process can further include forming a lower electrode ofa capacitor, on the substrate.

In the first mask process, the lower electrode of the capacitor can beformed on a same layer as the source electrode and the drain electrodeof the TFT, at a same time as the source electrode and the drainelectrode of the TFT.

The second mask process can further include forming an upper electrodeon the lower electrode of the capacitor.

In the second mask process, the upper electrode of the capacitor can beformed on a same layer as the gate electrode of the TFT, at a same timeas the gate electrode of the TFT.

The first mask process can be performed by using a half-tone mask.

The active layer, the source electrode, and the drain electrode of theTFT can be integrally formed.

At least a portion of the active layer can overlap the source electrode,the drain electrode, and the gate electrode. The active layer caninclude a first region which is an area overlapping the source electrodeand the drain electrode, a second region which is an area overlappingthe gate electrode, and a third region which is an area except the firstregion and the second region, wherein the first region is formed suchthat the active layer directly contacts the source electrode and thedrain electrode.

The method can further include, between the second mask process and thethird mask process, disposing impurities only in the third region of theactive layer.

Another aspect is a thin film transistor (TFT) array substrate for adisplay device, the TFT array substrate comprising a substrate and a TFTformed over the substrate and comprising an active layer, a gateelectrode, a source electrode, a drain electrode, a first insulatinglayer interposed between the gate electrode and the source and drainelectrodes, wherein each of the source and drain electrodes isinterposed between the active layer and the first insulating layer. TheTFT array substrate also comprises a capacitor formed over the substrateand having lower and upper electrodes and a pixel electrode electricallyconnected to the TFT.

In the above array substrate, the lower electrode of the capacitor isformed of the same material as that of the source and drain electrodesand formed on the same layer as the source and drain electrodes, whereinthe upper electrode of the capacitor is formed on the same layer as thegate electrode and formed of the same material as that of the gateelectrode.

In the above array substrate, the active layer has a first region atleast partially overlapping the source and drain electrodes, a secondregion at least partially overlapping the gate electrode, and a thirdregion different from the first and second regions, wherein only thethird region includes doped impurities.

In the above array substrate, the first region includes an area in whichthe active layer directly contacts the source and drain electrodes.

In the above array substrate, the first insulating layer covers theactive layer, the source electrode and the drain electrode.

In the above array substrate, the gate electrode is formed over thefirst insulating layer.

In the above array substrate, the active layer, the source electrode,and the drain electrode are integrally formed.

The TFT array substrate further comprises a second insulating layerwhich is formed over the TFT and the capacitor so as to cover the gateelectrode and the upper electrode of the capacitor.

Another aspect is an organic light-emitting diode (OLED) displaycomprising a substrate and a thin film transistor (TFT) formed over thesubstrate and comprising an active layer, a gate electrode, a sourceelectrode, a drain electrode, a first insulating layer interposedbetween the gate electrode and the source and drain electrodes, whereineach of the source and drain electrodes are interposed between theactive layer and the first insulating layer. The OLED display alsocomprises a capacitor formed over the substrate and comprising a lowerelectrode formed on the same layer as the source and drain electrodesand an upper electrode formed on the same layer as the gate electrode.The OLED display also comprises a second insulating layer formed overthe TFT and the capacitor so as to cover the gate electrode and theupper electrode. The OLED display also comprises a pixel electrodeelectrically connected to the TFT, a third insulating layer exposing acentral portion of the pixel electrode and covering an edge of the pixelelectrode, an intermediate layer formed over the pixel electrode andcomprising an emission layer, and an opposite electrode covering theintermediate layer and facing the pixel electrode.

In the above display, the active layer has a first region at leastpartially overlapping the source and drain electrodes, a second regionat least partially overlapping the gate electrode, and a third regiondifferent from the first and second regions, wherein only the thirdregion includes doped impurities.

Another aspect is a method of manufacturing an organic light-emittingdiode (OLED) display, the method comprising first forming asemiconductor material layer and a first metal layer over a substrate,wherein the first metal layer is formed over the semiconductor materiallayer. The method also includes first patterning the semiconductormaterial layer and the first metal layer so as to form an active layer,a source electrode, and a drain electrode of a thin film transistor(TFT). The method also includes second forming a first insulating layerincluding a portion corresponding to the active layer and third forminga second metal layer over the active layer, the source electrode and thedrain electrode. The method also includes second patterning the secondmetal layer so as to form a gate electrode on the portion of the firstinsulating layer and fourth forming a second insulating layer, having avia hole, over the first insulating layer so as to cover the gateelectrode, wherein the via hole exposes one of the source and drainelectrodes. The method also includes fifth forming a third metal layerover the second insulating layer, third patterning the third metal layerso as to form a pixel electrode electrically connected to one of thesource and drain electrodes through the via hole, and sixth forming athird insulating layer over the second insulating layer so as to coveredges of the pixel electrode and expose the remaining portion of thepixel electrode.

In the above method, the first forming and the first patterning areperformed with a first mask, wherein the second forming, the thirdforming and second patterning are performed with a second mask, whereinthe fourth forming is performed with a third mask, wherein the fifthforming and the fifth patterning are performed with a fourth mask, andwherein the sixth forming is performed with a fifth mask.

In the above method, the first forming comprises forming a lowerelectrode of a capacitor over the substrate.

In the above method, in the first forming, the lower electrode of thecapacitor is formed on the same layer as the source and drainelectrodes, and formed substantially simultaneously as the source anddrain electrodes.

In the above method, the second forming further comprises forming anupper electrode of the capacitor over the lower electrode.

In the above method, in the second forming, the upper electrode of thecapacitor is formed on the same layer as that of the gate electrode andformed substantially simultaneously as the gate electrode.

In the above method, the first forming is performed with a half-tonemask.

In the above method, the active layer, the source electrode, and thedrain electrode are integrally formed.

In the above method, the active layer has a first region at leastpartially overlapping the source and drain electrodes, a second regionat least partially overlapping the gate electrode, and a third regiondifferent from the first and second regions, wherein the first region isformed such that the active layer directly contacts the source and drainelectrodes.

The above method further comprises, between the third forming and thefourth forming, forming impurities only in the third region of theactive layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an OLED display including a thinfilm transistor (TFT) array substrate, according to an embodiment.

FIGS. 2A and 2B are cross-sectional views for describing a first maskprocess for manufacturing the OLED display of FIG. 1.

FIG. 3 is a cross-sectional view for describing a second mask processfor manufacturing the OLED display of FIG. 1;

FIG. 4 is a cross-sectional view for describing a third mask process formanufacturing the OLED display of FIG. 1.

FIG. 5 is a cross-sectional view for describing a fourth mask processfor manufacturing the OLED display of FIG. 1.

FIG. 6 is a cross-sectional view for describing a fifth mask process formanufacturing the OLED display of FIG. 1.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

In manufacturing OLED displays using photolithography, masks forpatterning have to be prepared. Thus, mask manufacturing costs increaseas more masks are used. Also, the patterning process can be verycomplicated, which also leads to increased manufacturing time and costs.

Reference will now be made in detail to exemplary embodiments, examplesof which are illustrated in the accompanying drawings, wherein likereference numerals refer to like elements throughout. In this regard,the present exemplary embodiments can have different forms and shouldnot be construed as being limited to the descriptions set forth herein.Accordingly, the exemplary embodiments are merely described below, byreferring to the figures, to explain aspects of the present description.As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items.

It will be understood that although the terms “first,” “second,” etc.can be used herein to describe various components, these componentsshould not be limited by these terms. These components are only used todistinguish one component from another.

It will be further understood that the terms “comprises” and/or“comprising” used herein specify the presence of stated features orcomponents, but do not preclude the presence or addition of one or moreother features or components. It will be understood that when a layer,region, or component is referred to as being “formed on,” another layer,region, or component, it can be directly or indirectly formed on theother layer, region, or component. That is, for example, interveninglayers, regions, or components can be present.

Sizes of elements in the drawings can be exaggerated for convenience ofexplanation. In other words, since sizes and thicknesses of componentsin the drawings are arbitrarily illustrated for convenience ofexplanation, the following embodiments are not limited thereto.

In the following examples, the x-axis, the y-axis and the z-axis are notlimited to three axes of the rectangular coordinate system, and can beinterpreted in a broader sense. For example, the x-axis, the y-axis, andthe z-axis can be perpendicular to one another, or can representdifferent directions that are not perpendicular to one another.

When a certain embodiment can be implemented differently, a specificprocess order can be performed differently from the described order. Forexample, two consecutively described processes can be performedsubstantially at the same time or performed in an order opposite to thedescribed order. In this disclosure, the term “substantially” includesthe meanings of completely, almost completely or to any significantdegree under some applications and in accordance with those skilled inthe art. Moreover, “formed on” can also mean “formed over.” The term“connected” can include an electrical connection.

FIG. 1 is a cross-sectional view of an OLED display including a thinfilm transistor (TFT) array substrate, according to an embodiment.

Referring to FIG. 1, the OLED display according to the presentembodiment includes a substrate 100, a TFT formed on the substrate 100,a capacitor (CAP) including a lower electrode 145 and an upper electrode165, and a pixel electrode 210 electrically connected with the TFT.

The substrate 100 can be formed of various materials, such as a glassmaterial, a metal material, or a plastic material, such as polyethylenterephthalate (PET), polyethylen naphthalate (PEN), and polyimide. Thesubstrate 100 can have a display region in which a plurality of pixelsare formed and an ambient or non-display region which surrounds thedisplay region.

Devices, such as the TFT and the CAP, can be formed on the substrate100. In addition, an OLED 200 electrically connected to the TFT can beformed on the substrate 100. The pixel electrode 210 is electricallyconnected to the TFT.

The TFT includes an active layer 120 formed of amorphous silicon,polycrystalline silicon, or an organic semiconductor material, a sourceelectrode 140, a drain electrode 142, and a gate electrode 160.

A buffer layer 110 formed of silicon oxide (SiO₂) or silicon nitride(SiN_(x)) can be formed on the substrate 100 to planarize a surface ofthe substrate 100 or to prevent impurities from penetrating into theactive layer 120, and the active layer 120 can be formed on the bufferlayer 110.

The source electrode 140 and the drain electrode 142 can be formed onthe active layer 120. The source electrode 140 and the drain electrode142 directly contact a portion of the active layer 120 to beelectrically connected with the active layer 120. That is, there is noinsulating layer between the source electrode 140 and the drainelectrode 142, and the active layer 120, and thus, the source electrode140 and the drain electrode 142 are not electrically connected with theactive layer 120 via a contact hole formed in the insulating layer. Thesource electrode 140 and the drain electrode 142 directly contact theactive layer 120 to be integrally formed with the active layer 120. Inorder for the source and drain electrodes 140 and 142 to haveconductivity, the source and drain electrodes 140 and 142 can be formedof at least one material selected from, for example, Al, Pt, Pd, Ag, Mg,Au, Ni, Nd, Ir, Cr, Li, Ca, Mo, Ti, W, and Cu, as a single layer ormultiple layers.

The gate electrode 160 is formed above the active layer 120. The sourceelectrode 140 and the drain electrode 142 are electrically connected toeach other according to a signal applied to the gate electrode 160.Considering adhesion to an adjacent layer, surface flatness of a stackedlayer, and processability, the gate electrode 160 can be formed of atleast one material selected from, for example, Al, Pt, Pd, Ag, Mg, Au,Ni, Nd, Ir, Cr, Li, Ca, Mo, Ti, W, and Cu, as a single layer or multiplelayers.

Here, in order to secure insulation between the active layer 120 and thegate electrode 160, a first insulating layer 130, which is a gateinsulating layer formed of silicon oxide (SiO₂) and/or silicon nitride(SiN_(x)), can be interposed between the active layer 120 and the gateelectrode 160. The first insulating layer 130 can also be interposedbetween the gate electrode 160, and the source and drain electrodes 140and 142. The source and drain electrodes 140 and 142 are formed betweenthe active layer 120 and the first insulating layer 130. As illustratedin FIG. 1, the first insulating layer 130 can be formed to cover notonly the active layer 120 but also the source and drain electrodes 140and 142, and the gate electrode 160 can be formed on the firstinsulating layer 130.

Meanwhile, as described above, the source electrode 140, the drainelectrode 142, and the gate electrode 160 can be formed on the activelayer 120, and thus, at least a portion of the active layer 120 overlapsthe source electrode 140, the drain electrode 142, and the gateelectrode 160. Here, the active layer 120 can have a first region 122which is an area overlapping the source and drain electrodes 140 and142, a second region 124 which is an area overlapping the gate electrode160, and a third region 126 which is an area except the first and secondregions 122 and 124. Here, the first region 122 can be the region inwhich the active layer 120 overlaps and directly contacts the source anddrain electrodes 140 and 142.

The active layer 120 includes an impurity region doped with impuritiesand a channel region not doped with impurities. In some embodiments,only the third region 126 is doped with impurities, and thus, the thirdregion 126 can be the impurity region. Accordingly, in some embodiments,the first region 122 does not include impurities. Likewise, the secondregion 124 corresponding to a portion of the active layer 120, can beunderstood as the channel region, and can have a semiconductorcharacteristic.

Meanwhile, a second insulating layer 170 can be formed above the gateelectrode 160. The second insulating layer 170 can be formed to coverthe active layer 120, the source electrode 140, and the drain electrode142. In this case, the second insulating layer 170 can be a protectivelayer. When the OLED 200 is formed above the TFT, the second insulatinglayer 170 can be a planarization layer for substantially planarizing anupper surface of the TFT. The second insulating layer 170 can be formedof silicon oxide (SiO₂) or silicon nitride (SiN_(x)), as a single layeror multiple layers. FIG. 1 illustrates the second insulating layer 170as a single layer. However, various alternations are possible. That is,the second insulating layer 170 can be multiple layers.

The CAP can be formed at a side of the TFT. The CAP includes the lowerelectrode 145 and the upper electrode 165. An insulating layerelectrically separating the lower and upper electrodes 145 and 165 canbe interposed between the lower electrode 145 and the upper electrode165.

The lower electrode 145 can be formed of the same material as that ofthe source and drain electrodes 140 and 142 and can be formed on thesame layer as the source and drain electrodes 140 and 142. Accordingly,the source and drain electrodes 140 and 142 and the lower electrode 145can be formed by the same mask process.

Meanwhile, the lower electrode 145 can be formed directly on the bufferlayer 110. In some embodiments, an auxiliary layer 125 is further formedbelow the lower electrode 145, as illustrated in FIG. 1. The auxiliarylayer 125 can be formed of the same material as that of the active layer120 and can be formed on the same layer as the active layer 120. Thatis, the auxiliary layer 125 can be formed of amorphous silicon,polycrystalline silicon, or an organic semiconductor material.

The upper electrode 165 can be formed on the same layer as the gateelectrode 160 and can be formed of the same material as that of the gateelectrode 160. Accordingly, the gate electrode 160 and the lowerelectrode 145 can be formed by the same mask process.

The first insulating layer 130 can be interposed between the lower andupper electrodes 145 and 165. Although FIG. 1 illustrates the firstinsulating layer 130 as a single layer, the first insulating layer 130can have a multi-layered structure and other variations are possible.Thus, in the CAP according to the present embodiment, an electricalcapacity can be increased, since the first insulating layer 130functions as a dielectric layer and the CAP is formed as ametal-insulator-metal (MIM) CAP, in which both of the lower and upperelectrodes 145 and 165 are formed of a metal.

The second insulating layer 170 can be formed on the upper electrode 165to cover the upper electrode 165. The second insulating layer 170 cancover the TFT and the CAP to protect the TFT and the CAP and cansubstantially planarize the surface on which the OLED 200 is formed, asdescribed above.

The OLED 200 having the pixel electrode 210, an opposite electrode 230facing the pixel electrode 210, and an intermediate layer 220 interposedbetween the pixel electrode 210 and the opposite electrode 230 andincluding an emission layer, is formed on the second insulating layer170.

There is an opening portion exposing at least one of the source anddrain electrodes 140 and 142 in the second insulating layer 170. Thepixel electrode 210 contacting either of the source electrode 140 andthe drain electrode 142 via the opening portion to be electricallyconnected to the TFT is formed on the second insulating layer 170. Thepixel electrode 210 can be formed as a (half) transparent electrode or areflection electrode. When the pixel electrode 210 is formed as the(half) transparent electrode, the pixel electrode 210 can be formed of,for example, ITO, IZO, ZnO, In₂O₃, IGO, or AZO. When the pixel electrode210 is formed as the reflection electrode, the pixel electrode 210 caninclude a reflective layer formed of Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir,Cr, or a combination thereof, and a layer formed of ITO, IZO, ZnO,In₂O₃, IGO, or AZO. However, embodiments are not limited thereto. Thepixel electrode 210 can be formed of various materials and also, thestructure of the pixel electrode 210 can vary. For example, the pixelelectrode 210 is formed as a single layer or multiple layers.

A third insulating layer 180 can be formed on the second insulatinglayer 170. The third insulating layer 180 is a pixel-defining layer. Thethird insulating layer 180 has openings respectively corresponding tosub-pixels, that is, the openings covering an edge of the pixelelectrode 210 so as to expose a central portion of each of the pixelelectrode 210, so that the third insulating layer 180 can define pixels.Also, as illustrated in FIG. 1, the third insulating layer 180 increasesthe distance between ends of the pixel and opposite electrodes 210 and230, thereby preventing an arc forming in the end of the pixel electrode210. The third insulating layer 180 can be formed of, for example, anorganic material, such as polyimide.

The intermediate layer 220 of the OLED 200 can be formed of a lowmolecular weight material or a high molecular weight material. When theintermediate layer 220 is formed of the low molecular weight material, ahole injection layer (HIL), a hole transport layer (HTL), an electrontransport layer (ETL), and an electron injection layer (EIL) can bestacked below or above an emission layer (EML), as a single-layered or amulti-layered structure. Also, the intermediate layer 220 can be formedof various organic materials, such as copper phthalocyanine (CuPc),N,N′-Di(naphthalene-1-yl)-N, N′-diphenyl-benzidine (NPB), andtris-8-hydroxyquinoline aluminum (Alq3). The HIL, the HTL, the ETL, theEIL, and the EML can be formed by using a vapor deposition method.

When the intermediate layer 220 includes the high molecular weightmaterial, the intermediate layer 220 can usually have a structureincluding the HTL and the EML. Here, PEDOT can be used for the HTL, anda high molecular weight material, such as poly-phenylenevinylene (PPV)and polyfluorene, can be used for the EML. Here, screen printing, inkjetprinting, or laser induced thermal imaging (LITI) can be used to formthe HTL and the EML. The intermediate layer 220 is not necessarilylimited thereto, and can have various structures.

The opposite electrode 230 can be formed to face the pixel electrode 210with the intermediate layer 220 including the EML between the oppositeelectrode 230 and the pixel electrode 210. Although it is notillustrated in FIG. 1, the opposite electrode 230 can be formedthroughout the substrate 100. That is, the opposite electrode 230 can beintegrally formed with the OLED 200 so as to correspond to the pixelelectrode 210.

The opposite electrode 230 can be formed as a (half) transparentelectrode or a reflection electrode. When the opposite electrode 230 isformed as the (half) transparent electrode, the opposite electrode 230can have a layer formed of a metal having a high work function, such asLi, Ca, LiF/Ca, LiF/Al, Al, Ag, Mg, or a combination thereof, and a(half) transparent conductive layer, such as ITO, IZO, ZnO, or In₂O₃.When the opposite electrode 230 is formed as the reflection electrode,the opposite electrode 230 can have a layer formed of Li, Ca, LiF/Ca,LiF/Al, Al, Ag, Mg, or a combination thereof. The structure and thematerial of the opposite electrode 230 are not limited thereto, andvarious alterations are possible.

The TFT array substrate and the OLED display including the TFT arraysubstrate are described. However, the described technology is notlimited thereto. That is, a method of manufacturing the OLED display isalso included in the scope of the described technology.

FIGS. 2A and 2B are cross-sectional views for describing a first maskprocess for manufacturing the OLED display of FIG. 1.

Referring to FIGS. 2A and 2B, the active layer 120, the source electrode140, and the drain electrode 142 of the TFT can be formed bysequentially spreading a semiconductor material layer 120′ and a firstmetal layer 140′ on the substrate 100 and patterning the semiconductormaterial layer 120′ and the first metal layer 140′. Here, before thesemiconductor material layer 120′ and the first metal layer 140′ areformed on the substrate 100, the buffer layer 110 can be formed on thesubstrate 100.

As illustrated in FIG. 2A, a photoresist 150 is spread on the firstmetal layer 140′ to pattern the semiconductor material layer 120′ andthe first metal layer 140′, and then, the active layer 120, the sourceelectrode 140, and the drain electrode 142 can be substantiallysimultaneously patterned by a photolithography process using a firstmask (not shown). The patterning process of the photolithography methodincludes a series of processes including light exposure, development,etching, and scrip or ashing. This aspect will not be repeatedlydescribed, when sequential mask processes are described. Through thispatterning process, the active layer 120, the source electrode 140, andthe drain electrode 142 can be patterned as illustrated in FIG. 2B.

As described above, the active layer 120, the source electrode 140, andthe drain electrode 142 can be substantially simultaneously patternedthrough the first mask process. In order to substantially simultaneouslypattern material layers having height differences by using one mask, ahalf-tone mask can be used as the first mask. Using the process usingthe half-tone mask, the active layer 120, the source electrode 140, andthe drain electrode 142 can be integrally formed.

Here, in the first mask process, the auxiliary layer 125 and the lowerelectrode 145 of the CAP can be formed together with the active layer120, the source electrode 140, and the drain electrode 142 of the TFT.Thus, the lower electrode 145 can be substantially simultaneously formedwith and on the same layer as the source and drain electrodes 140 and142. The auxiliary layer 125 can be substantially simultaneously formedwith and on the same layer as the active layer 120.

FIG. 3 is a cross-sectional view for describing a second mask processfor manufacturing the OLED display of FIG. 1.

Referring to FIG. 3, the first insulating layer 130 is stacked on theactive layer 120, the source electrode 140, and the drain electrode 142to cover the active layer 120, the source electrode 140, and the drainelectrode 142 of the TFT. The first insulating layer 130 can be a gateinsulating layer separating the active layer 120 and the gate electrode160.

After a second metal layer (not shown) is stacked on the firstinsulating layer 130, the second metal layer can be patterned to formthe gate electrode 160 on a portion of the first insulating layer 130,which corresponds to the active layer 120.

Here, the upper electrode 165 can be formed on the lower electrode 145of the CAP, substantially simultaneously with the gate electrode 160.Thus, the upper electrode 165 can be formed of the same material as thatof the gate electrode 160 and can be formed substantially simultaneouslywith and on the same layer as the gate electrode 160. The firstinsulating layer 130 can be interposed between the lower and upperelectrodes 145 and 165 as a dielectric layer.

The semiconductor material layer 120′ can be formed of amorphoussilicon, crystalline silicon, or a transparent conductive oxidesemiconductor. When the semiconductor material layer 120′ is formed ofamorphous silicon, a process of crystallizing amorphous silicon canfurther be included. The method of crystallizing amorphous silicon caninclude a rapid thermal annealing (RTA) method, a solid phasecrystallization (SPC) method, an excimer laser annealing (ELA) method, ametal induced crystallization (MIC) method, a metal induced lateralcrystallization (MILC) method, and a sequential lateral solidification(SLS) method.

Here, at least a portion of the active layer 120 overlaps the sourceelectrode 140, the drain electrode 142, and the gate electrode 160. Theactive layer 120 can have the first to third regions 122, 124 and 126.In the first region 122, the active layer 120 can directly contact thesource and drain electrodes 140 and 142. The second region 124 can be achannel region and the third region 126 can be an impurity region.

In order to form the third region 126 as the impurity region, the thirdregion 126 can be doped in portions of the first insulating layer 130 asindicated by the letter D, after the gate electrode 160 is formed.Depending on the materials used in doping, the active layer 120 of theTFT can be an n-type semiconductor or a p-type semiconductor.

FIGS. 4 through 6 are cross-sectional views for describing a third maskprocess through a fifth mask process for manufacturing the OLED displayof FIG. 1.

Referring to FIG. 4, in the third mask process, a via-hole exposing atleast one of the source and drain electrodes 140 and 142 of the TFT isformed after the second insulating layer 170 is stacked on the firstinsulating layer 130 to cover the gate electrode 160. The secondinsulating layer 170 can be a protective layer protecting the TFT andthe CAP or a planarization layer substantially planarizing a surface onwhich the OLED 200 is formed. Although FIG. 4 illustrates the secondinsulating layer 170 as a single layer, various alterations arepossible. That is, the second insulating layer 170 can be formed asmultiple layers.

Next, referring to FIG. 5, in the fourth mask process, the pixelelectrode 210 which is electrically connected to one of the source anddrain electrodes 140 and 142 via the via-hole can be formed, after athird metal layer (not shown) is spread on the second insulating layer170.

Then, referring to FIG. 6, in the fifth mask process, the thirdinsulating layer 180 exposing a central portion of the pixel electrode210 by covering an edge of the pixel electrode 210 can be formed on thesecond insulating layer 170. The third insulating layer 180 can be apixel-defining layer defining a pixel region.

Although it is not illustrated in FIG. 6, referring again to FIG. 1, theintermediate layer 220 including the EML can be formed on the pixelelectrode 210, and the opposite electrode 230 covering the intermediatelayer 220 can be formed on the third insulating layer 180.

As described above, according to at least one of the disclosedembodiments, the number of masks can be reduced in a process ofmanufacturing the OLED display. Thus, the manufacturing process becomessimpler. Also, since the first insulating layer 130, which correspondsto a gate insulating layer, is formed between the source and drainelectrodes 140 and 142 and the gate electrode 160, the CAP can have ametal/insulator/metal (MIM) structure, which is a stable structure. Inaddition, since the gate electrode 160, the source and drain electrodes140 and 142, and the pixel electrode 210 are each separately etched,wet-etching can be easily performed and there is little etch skew afteretching, thereby significantly reducing resistance of wirings.

It should be understood that the exemplary embodiments described thereinshould be considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each exemplaryembodiment should typically be considered as available for other similarfeatures or aspects in other exemplary embodiments.

While the inventive technology has been described with reference to thefigures, it will be understood by those of ordinary skill in the artthat various changes in form and details can be made therein withoutdeparting from the spirit and scope as defined by the following claims.

What is claimed is:
 1. A thin film transistor (TFT) array substrate fora display device, the TFT array substrate comprising: a substrate; a TFTformed over the substrate and comprising an active layer, a gateelectrode, a source electrode, a drain electrode, a first insulatinglayer interposed between the gate electrode and the source and drainelectrodes, wherein each of the source and drain electrodes isinterposed between the active layer and the first insulating layer; acapacitor formed over the substrate and having lower and upperelectrodes; and a pixel electrode electrically connected to the TFT. 2.The TFT array substrate of claim 1, wherein the lower electrode of thecapacitor is formed of the same material as that of the source and drainelectrodes and formed on the same layer as the source and drainelectrodes, and wherein the upper electrode of the capacitor is formedon the same layer as the gate electrode and formed of the same materialas that of the gate electrode.
 3. The TFT array substrate of claim 1,wherein the active layer has a first region at least partiallyoverlapping the source and drain electrodes, a second region at leastpartially overlapping the gate electrode, and a third region differentfrom the first and second regions, and wherein only the third regionincludes doped impurities.
 4. The TFT array substrate of claim 3,wherein the first region includes an area in which the active layerdirectly contacts the source and drain electrodes.
 5. The TFT arraysubstrate of claim 4, wherein the first insulating layer covers theactive layer, the source electrode and the drain electrode.
 6. The TFTarray substrate of claim 5, wherein the gate electrode is formed overthe first insulating layer.
 7. The TFT array substrate of claim 1,wherein the active layer, the source electrode, and the drain electrodeare integrally formed.
 8. The TFT array substrate of claim 1, furthercomprising a second insulating layer which is formed over the TFT andthe capacitor so as to cover the gate electrode and the upper electrodeof the capacitor.
 9. An organic light-emitting diode (OLED) displaycomprising: a substrate; a thin film transistor (TFT) formed over thesubstrate and comprising an active layer, a gate electrode, a sourceelectrode, a drain electrode, a first insulating layer interposedbetween the gate electrode and the source and drain electrodes, whereineach of the source and drain electrodes are interposed between theactive layer and the first insulating layer; a capacitor formed over thesubstrate and comprising a lower electrode formed on the same layer asthe source and drain electrodes and an upper electrode formed on thesame layer as the gate electrode; a second insulating layer formed overthe TFT and the capacitor so as to cover the gate electrode and theupper electrode; a pixel electrode electrically connected to the TFT; athird insulating layer exposing a central portion of the pixel electrodeand covering an edge of the pixel electrode; an intermediate layerformed over the pixel electrode and comprising an emission layer; and anopposite electrode covering the intermediate layer and facing the pixelelectrode.
 10. The OLED display of claim 9, wherein the active layer hasa first region at least partially overlapping the source and drainelectrodes, a second region at least partially overlapping the gateelectrode, and a third region different from the first and secondregions, and wherein only the third region includes doped impurities.11. A method of manufacturing an organic light-emitting diode (OLED)display, the method comprising: first forming a semiconductor materiallayer and a first metal layer over a substrate, wherein the first metallayer is formed over the semiconductor material layer; first patterningthe semiconductor material layer and the first metal layer so as to forman active layer, a source electrode, and a drain electrode of a thinfilm transistor (TFT); second forming a first insulating layer includinga portion corresponding to the active layer; third forming a secondmetal layer over the active layer, the source electrode and the drainelectrode; second patterning the second metal layer so as to form a gateelectrode on the portion of the first insulating layer; fourth forming asecond insulating layer, having a via hole, over the first insulatinglayer so as to cover the gate electrode, wherein the via hole exposesone of the source and drain electrodes; fifth forming a third metallayer over the second insulating layer; third patterning the third metallayer so as to form a pixel electrode electrically connected to one ofthe source and drain electrodes through the via hole; and sixth forminga third insulating layer over the second insulating layer so as to coveredges of the pixel electrode and expose the remaining portion of thepixel electrode.
 12. The method of claim 11, wherein the first formingand the first patterning are performed with a first mask, wherein thesecond forming, the third forming and second patterning are performedwith a second mask, wherein the fourth forming is performed with a thirdmask, wherein the fifth forming and the fifth patterning are performedwith a fourth mask, and wherein the sixth forming is performed with afifth mask.
 13. The method of claim 11, wherein the first formingcomprises forming a lower electrode of a capacitor over the substrate.14. The method of claim 13, wherein, in the first forming, the lowerelectrode of the capacitor is formed on the same layer as the source anddrain electrodes, and formed substantially simultaneously as the sourceand drain electrodes.
 15. The method of claim 11, wherein the secondforming further comprises forming an upper electrode of the capacitorover the lower electrode.
 16. The method of claim 15, wherein, in thesecond forming, the upper electrode of the capacitor is formed on thesame layer as that of the gate electrode and formed substantiallysimultaneously as the gate electrode.
 17. The method of claim 11,wherein the first forming is performed with a half-tone mask.
 18. Themethod of claim 11, wherein the active layer, the source electrode, andthe drain electrode are integrally formed.
 19. The method of claim 11,wherein the active layer has a first region at least partiallyoverlapping the source and drain electrodes, a second region at leastpartially overlapping the gate electrode, and a third region differentfrom the first and second regions, and wherein the first region isformed such that the active layer directly contacts the source and drainelectrodes.
 20. The method of claim 19, further comprising, between thethird forming and the fourth forming, forming impurities only in thethird region of the active layer.